Various roof membranes are well-known in the art, the most commonly used being so-called single ply materials. In general, these single ply materials may be separated into four classes: modified bitumens; thermoplastics; elastomerics; and uncured elastomers. The modified bitumen group includes various membranes having an asphalt or coal tar content in them. They may also contain polymer additives or modifiers as well as various types of reinforcement (either within the membrane or its surface). The thermoplastic-type membranes are primarily polyvinyl chloride (PVC) or any sheet which has PVC as a principal polymer. They also include other thermoplastic polymers alloyed with PVC. The elastomers are predominantly ethylene propylene diene monomer (EPDM) with neoprene following in the order of usage. The materials are essentially thermosets or cured (or vulcanized) membranes which cannot be welded together. They can only be spliced with contact or tape adhesives. The uncured elastomers are materials which come to the roof in a thermoplastic state and can be solvent or heat welded for lap joint construction. They slowly cure or cross-link due to the sun's radiation and become elastomers in place, on the roof.
Since these general classes of roofing membranes are well-known and per se comprise no part of this invention, they need not be described in greater detail.
Generally, roof membranes can be used in four different types of roof system assemblies: loose laid/ballasted; partially adhered (or mechanically attached); fully adhered; and the protected roof membrane assembly.
Irrespective of the means of installation, where the membrane is of insufficient size to cover the roof, it will be appreciated that two or more membranes must be employed. For optimum protection against moisture and/or other environmental conditions, these multiple membranes should be seamed together. While the membranes could be butted together along adjacent edges and then sealed, the most efficacious way is to provide a lap joint wherein one edge of a membrane covers or overlaps the adjacent edge of another membrane.
the present invention relates to improved construction of a roof membrane, e.g. a previously known membrane, to provide a superior lap joint between two adjacent membranes. Since, as mentioned earlier, EPDM and other elastomers can only be seamed or spliced with contact or tape adhesives, the invention is particularly directed to roofing membranes of this description and will accordingly be discussed hereinafter for purposes of illustration by reference thereto. In recent years, EPDM has become very popular as a roof membrane. According to the "1984 Handbook of Single-Ply Roofing Systems", published by Harcourt Brace Jovanovich Publications, there were nineteen (19) different manufacturers offering fifty-one (51) different EPDM membranes.
by way of illustration, mention may be made of the "POLYKEN" (trademark of The Kendall Company) Roofing Systems utilizing a black EPDM 45 mils thick, having a weight/sq. ft. of 0.28 lb, and commercially available in 7, 10, 20, 30, 40 and 100 foot widths. Irrespective of the system of installation and the insulation or other substrate on which it is laid, adjacent sheets should be lap joined, e.g. with a tape which of course should be two-faced.
Pressure-sensitive adhesives of known formulation are particularly suitable for this purpose, an especially useful one being a butyl rubber-based adhesive. The tape may comprise a suitable support sheet having an adhesive layer on each surface or it may comprise a single adhesive layer of of appropriate thickness, e.g. on the order of 40 mils. Preferably, a release sheet is provided on at least one surface so that the tape may be provided in roll form.
If found desirable to do so, the periphery of the membrane may be provided with a primer coat to increase cohesion with the particular tape employed. However, when employing rubber-rubber bonds, that is, when a butyl rubber or other rubber-based tape is employed with an EPDM membrane, such primer coatings have not been found to be necessary.
An EPDM membrane of the foregoing description may be installed by any of the aforementioned systems, namely, loose-laid/ballast, partial attachment, fully adhered, or by protective membrane roofing assembly, as desired. It may be employed for re-roofing or as a new roofing over various insulation materials including perlite, urethane, wood fiber, fiberglass, expanded polystyrene, composite boards, cellular glass, extruded polystyrene, and the like.
Regardless of the method of installation, if a single sheet is not sufficient to cover the roof, a lap joint will be made with one or more adjacent sheets. If two or more sheets of sufficient length are to be laid side by side, one lateral edge of one sheet will overlap the adjacent lateral edge of the next adjacent sheet. In like manner, if two (or more) sheets are to be laid end to end, the end portions of adjacent sheets will provide a lap joint, e.g. laying the trailing end portion of one sheet over the leading end portion of the next adjacent sheet. In any event, the lap joint will typically be on the order of at least three inches.
Following the laying of the membranes in the foregoing manner, the overlapping portion is then peeled back, a roll of the two-sided pressure-sensitive tape (typically with a release sheet on one side) is then adhered to the exposed surface of the underlying sheet edge, after which the release sheet is removed from the free surface of the tape and the top sheet is then repositioned so that the top (free) surface of the tape is adhered to the underside of the overlapping sheet, thereby completing the lap joint.
While in theory, the lap joint seal should be entirely satisfactory over a prescribed time period and under the expected or usual environmental conditions, it has been found that this is not always the case.
Specifically, it has been found that, following installation of the roofing system, environmental forces such as temperature changes and wind drag cause certain degradative changes in the lap joint.
These degradative changes are manifested as random separations or puckering along the lap joint which may be termed "fish-mouth" resulting from Poisson's effect. These fish-mouth separations permit moisture to enter, which in turn will cause rotting and/or other adverse effects on the underlying roof material.
The present invention is directed to the task of materially reducing if not obviating the fish-mouth problem so as to increase substantially the longevity of the lap joint seal and thus materially increase the time period between installation and repair of the lap joint.